Tully-Fisher relation
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In astronomy, the Tully-Fisher relation, published by astronomers R. Brent Tully and J. Richard Fisher in 1977, is an empirical relationship between the intrinsic luminosity or stellar mass of a spiral galaxy and its velocity width (the amplitude of its rotation curve). The luminosity is the amount of light energy emitted by the galaxy per unit time; it can be measured using the galaxy's apparent brightness when the distance to the galaxy is known. The velocity width is measured via the width or shift of spectral lines and the Doppler effect.
The quantitative relationship between luminosity and velocity width is a function of the wavelength at which the luminosity is measured, but roughly speaking, the relation has luminosity proportional to velocity to the fourth power.
The relation connects the directly (and relatively easily) observable velocity width to the difficult-to-observe intrinsic luminosity. Because the luminosity is related to the (easily observed) apparent brightness by the distance (squared), the Tully-Fisher relation can be used as a distance measurement, or, in the astronomical parlance a "secondary standard candle".
Internal dynamics of stars in galaxies are driven by gravity. For this reason, the amplitude of the galaxy rotation curve is related to the galaxy's mass; the Tully-Fisher relation is a direct observation of a close relationship between galaxy stellar mass (which sets the luminosity) and total gravitational mass (which sets the amplitude of the rotation curve).
The relation is measured and calibrated using primary standard candles.
[edit] See also
- Distance modulus
- Modified Newtonian dynamics
- Standard candle
- Cosmic distance ladder
- Fundamental plane (elliptical galaxies)
- Faber-Jackson relation
[edit] References
- zebu.uoregon.edu/~imamura/209/apr7/TF.html
- Kuhn, Karl F., In Quest of the Universe. ISBN 0-314-02393-3.
- 2003 C-level Astronomy Presentation for Science Olympiad (Microsoft PowerPoint format, openable in OpenOffice.org)
- Tully, R. B.; Fisher, J. R., A new method of determining distances to galaxies. (pdf) Astronomy and Astrophysics, vol. 54, no. 3, Feb. 1977, p. 661-673. (abs)
- Macri, L. M.; K. Z. Stanek & D. Bersier et al. (2006), "A New Cepheid Distance to the Maser-Host Galaxy NGC 4258 and Its Implications for the Hubble Constant", Astrophysical Journal 652(2): 1133-1149
[edit] External links
- Stephens, Tim. "AEGIS survey reveals new principle governing galaxy formation and evolution", UC Santa Cruz, March 6, 2007. Retrieved on 2006-05-24.
